1. Field of the Invention
The invention relates to an EMI sleeve additionally used in the transceiver SFP (Small Form Factor Pluggable), and particularly to the structural relation between the existing insulative sleeve and the new EMI metallic sleeve attached upon the insulative sleeve.
2. Description of Related Art
As cost-pressures increase, it is pretty standard practice now for plastic optical lenses to be used in SFP+ and other transceivers as molded plastic piece parts tend to a lot cheaper than metal TO (transistor outline) can (TO-can) optical sub-assembly solutions. However, as data rates and port density increase, electromagnetic interference (EMI) is becoming more and more problematic. As shown in FIG. 15, in a typical SFP+ transceiver design, there is usually a metal housing 151 of some sort that encapsulates the electrical-optical subassemblies (EOSA) of the transceiver. An EMI collar 152 helps to reduce emissions from around the module. However, as the optics are usually made of plastic for cost reasons, the plastic lenses 153 create quite a large aperture 154 from which EMI emission can escape.
As shown in FIG. 16 which shows side by side a prior art design and a design in accordance with the present invention, in a typical SFP+ transceiver design on the left side of the drawing figure, the length of the leakage aperture is indicated by A1, the length A1 is much smaller than the length of the lenses, and the minimum aperture size B1 is substantially the same as the diameter of the lenses. At lower data rates the large apertures size was tolerable, but at data rate such at 25G or 28G the leakage is untenable. Thus there exists a great need to find a way to either decrease the aperture size, and/or increase the length through which the emissions must escape through as that will help to minimize their effect.
At the same time, the solution must be cheap, and also precise enough such that introducing an extra piece part does not cause the assembly to violate any FOCIS (Fiber Optic Connector Intermateability Standard) or MSA (Multi-source Agreement) specifications. It should be assured that the improved solution will work with all existing complementary optical connectors.
The invention relates to a solution to the aforementioned issue by using a deep drawn metallic EMI sleeve that will help to not only decrease the aperture (diametrical) size but also increase the shielding length through which the emission must radiate through, and further is able to meet FOCIS and MSA specification without compromising cable assembly interoperability thereof.